The present invention relates to a step difference detection apparatus used as, e.g., an apparatus for detecting the position and area of the address label or address indication cellophane window (address window) of mail, and a processing apparatus using the same.
Conventionally, to detect the region of an address label on the upper surface of a letter of, e.g., a mail envelope, the image on the upper surface of the mail item is simply sensed, and a rectangular region having an appropriate size and position, which appears to be an address label, is detected.
This method is effective to some degree but is influenced when letters have address labels and upper surfaces in the same color, or letters have label-like pictures on the upper surfaces.
Conventionally, to detect an address window (a window portion covered with a transparent sheet optically having a high reflection ratio, e.g., a cellophane or paraffine sheet), the positive reflected light component of illumination light is detected.
An example is disclosed in Jpn. Pat. Appln. KOKOKU Publication No. 58-45305 (Japanese Patent No. 1377041). This method is exclusively used to detect an address window. Address label detection must be performed using another method.
In addition, several step difference/unevenness detection methods applicable to detect an address label or an address window are conventionally known. As the first method, a shadow or scattered light due to a stepped edge is read by oblique illumination.
FIG. 1 shows an arrangement for reading the step difference on the upper surface of a letter by simple oblique illumination. This arrangement is incorporated in a culler facer canceller for automatically facing and canceling a lot of letters including mail envelopes and aims to detect the flap of a letter (folded seal portion of mail) for discrimination between the upper and lower surfaces of the letter. A similar arrangement is disclosed in Jpn. Pat. Appln. KOKOKU Publication No. 5-7750.
As shown in FIG. 1, a light beam emitted from a halogen lamp 1 is collimated by a collimator lens 2 to obliquely irradiate a letter 3 at a large incident angle (the incident angle means the angle formed by the normal and the incident light beam).
An image sensing means constituted by an image sensing lens (camera lens) 4 and a CCD sensor 5 senses the image of the letter from the vertical direction to detect a shadow 6 generated at the step portion, thereby detecting the position of the step difference of the flap.
However, the method of detecting the shadow or scattered light by simple oblique illumination may be influenced by the printed contents on the upper surface of the letter. For example, when a black straight line is printed on the upper surface of the letter, the output obtained upon reading this line can hardly be discriminated from that obtained by reading the edge of the address label on the upper surface of the letter or that obtained by reading the flap on the lower surface of the letter.
Another representative step difference detection apparatus using oblique illumination is SERRATION READER BML3D, shown in FIG. 2, available from SCHRACK in Australia. This is an edge detection apparatus exclusively used for stamps.
As shown in FIG. 2, in this apparatus, illumination light containing parallel light components obliquely illuminates a linear region on a surface with a stamp at a large incident angle. This region is read by a line image sensor. The read region (CCD AREA in FIG. 2) of the line image sensor is almost parallel to the longitudinal side of the stamp.
A portion corresponding to each punch hole of the perforation generates a shadow on the upper side of the hole due to the oblique illumination effect while the lower side of the hole scatters the illumination light and becomes bright. By reading this region, a signal having a period corresponding to the interval of the perforations of the stamp is obtained.
When this signal is collated with a predetermined reference pattern, the perforated edge of the stamp is detected. This method utilizes, at maximum, the fact that a stamp has notches of perforations, thereby improving the detection reliability. For this reason, this method cannot be applied to an address label having straight sides.
As still another surface unevenness detection method, triangulation shown in FIG. 3 is known. FIG. 3 is quoted from xe2x80x9cHandbook of Applied Opto-electronicsxe2x80x9d, Shoko-sha (1989). In FIG. 3, the point to be measured is irradiated with a laser beam emitted from a semiconductor laser light source 7 to obliquely observe the spot.
The spot forms an image on a position sensor 9 through an imaging lens 8. The position of the spot image on the position sensor changes depending on the height of the point to be measured. Therefore, when the change in spot image position is detected, the height of the point to be measured can be detected. Visible laser displacement sensors of LB-1000 series (LB-1000/LB-040) available from KEYENCE use this technique.
In this technique, only one point is measured in one measurement operation. To measure the unevenness of a region with a two-dimensional extent, like an address label, detection devices need be arrayed, and the letter must be carried under the array of detection devices. Since limitations are imposed on size reduction of individual sensors, this technique is disadvantageous in resolution power or cost.
As described above, in the conventional address label and address window detection apparatus or step difference detection apparatus using oblique illumination, a change in reflection ratio distribution due to printed contents on the upper surface of a letter or a background design influences the step difference reading result, so the step position cannot be properly detected.
In addition, the stamp edge detection method or unevenness detection based on triangulation cannot be directly applied to detect unevenness of a region having a two-dimensional extent and straight edges as in an address label.
The present invention has been made in consideration of the above situation, and has as its object to provide a step difference detection apparatus capable of minimizing the influence of the reflection ratio distribution on a measuring surface due to printed contents on the upper surface of a letter and highly precisely detecting the position of an address label or an address window on the upper surface of the letter, and a processing apparatus using the same.
In order to achieve the above object, according to the first aspect of the present invention, there is provided a step difference detection apparatus comprising:
illumination means for emitting illumination light;
incident means for making the illumination light emitted by the illumination means be incident on a plurality of small illumination regions on an object carried in a predetermined carrier direction from different directions;
image sensing means for inputting an image of the regions on the object illuminated with the illumination light which is made to be incident by the incident means; and
detection means for detecting a step difference on the object on the basis of the image sensed by the image sensing means.
In the step difference detection apparatus of the present invention, the object surface is divided into a plurality of small illumination regions each comprising a two-dimensional region, and adjacent small illumination regions are illuminated with illumination light from different directions, respectively.
By obtaining the image of the object comprising the small illumination regions using an image sensor or the like, the position of the step difference can be detected while almost eliminating the influence of the background design of the letter such as mail as the object.
For example, when a letter with an address label is illuminated obliquely with a collimated beam, a dark line or a bright line is formed at a stepped portion of the address label in accordance with the direction of the stepped portion due to the effect of oblique illumination.
In oblique illumination from the higher side of the step, a shadow is formed at the stepped portion. In oblique illumination from the lower side of the step, a bright line is formed at the stepped portion. At a portion having no step difference, the illuminance remains the same independently of the illumination direction.
As is apparent from the above description, an image obtained by oblique illumination from the right side is the same as that obtained by oblique illumination from the left side except that the bright and dark portions are inverted at the stepped portion. The image is sensed by illuminating adjacent small illumination regions from different directions, and a portion where the illuminance characteristically changes at the boundary between the small illumination regions is detected from the sensed image by image processing or the like. With this processing, the stepped portion corresponding to an edge of the address label can be detected.
More specifically, when a dark line in a small illumination region changes to a bright line in an adjacent small illumination region, the straight line is likely to be an edge of the address label.
Conversely, when a dark line in a small illumination region still remains dark in the adjacent small illumination region, and no discontinuous change in illuminance is observed at the boundary portions between the small illumination regions, the line is likely to be a simple black line printed on the upper surface of the letter.
Therefore, the position of an address label or an address window on the upper surface of the letter can be accurately detected without being influenced by the reflection ratio distribution due to the printed contents on the upper surface of the letter.
According to the second aspect of the present invention, there is provided a step difference detection apparatus comprising:
illumination means for illuminating an object with a plurality of types of illumination light beams having different characteristics from different directions;
beam splitting means for splitting a reflected light beam from the object into a plurality of light components in units of types of the illumination light beams using a difference in characteristics of the plurality of types of illumination light beams;
image sensing means for receiving the plurality of light components split by the beam splitting means and inputting a plurality of images corresponding to the plurality of types of illumination light beams, respectively; and
image processing means for processing the plurality of images input by the image sensing means to detect a step difference on the object.
The step difference detection apparatus of the present invention simultaneously illuminates the read region on the object, which is to be read by an image sensor or the like, with a plurality of types (preferably two types) of light beams having different characteristics from different directions.
The reflected light beam is resplit into the respective types of light components using the difference in characteristics of the light beams, thereby simultaneously sensing a plurality of images. By calculating the difference between the images, the step difference in the read plane is properly detected while eliminating the influence of the background design of the letter as the object.
When a letter with an address label is illuminated obliquely with a collimated beam, a shadow or a bright line is formed at a stepped portion of the address label in accordance with the direction of the stepped portion due to the effect of oblique illumination.
In oblique illumination from the higher side of the step, a shadow is formed at the stepped portion. In oblique illumination from the lower side of the step, a bright line is formed at the stepped portion. At a portion having no step difference, the illuminance remains the same independently of the illumination direction.
As is apparent from the above description, an image obtained by oblique illumination from the right side is the same as that obtained by oblique illumination from the left side except that the bright and dark portions are inverted at the stepped portion. When the difference between the two images is calculated in units of pixels, pieces of information of portions other than the stepped portion are offset, so the position information of the stepped portion can be obtained.
To calculate the difference, two images sensed under the same conditions except the illumination direction are required. In the present invention, this is realized by simultaneously illuminating the read region from the left and right sides and simultaneously sensing the two images.
However, to resplit the light beam from the two directions upon image sensing, light beams having a difference in some characteristics such as the wavelength or polarization direction are used as the left and right illumination light beams. Illumination is performed using these light beams, and the light beam is split into two light components using a beam splitting means such as a dichroic mirror before the light beam to be read is incident on the CCD line image sensor.
Depending on the printed contents on the upper surface of the letter, the transmission ratio may largely change due to the characteristics of light beams. However, in many cases, the reflection ratio difference can be sufficiently minimized by appropriately selecting the characteristics of the two light beams.
For example, to perform illumination using two light beams having different wavelengths, two light beams having wavelength relatively close to each other are used. When a light beam in a wavelength band where the reflection ratio for ink colors normally used for printing on the upper surface of the letter rarely changes, e.g., a light beam having a long wavelength such as infrared light is used, the reflection ratio difference can be sufficiently minimized even when the wavelengths of the two illumination light beams are not so close.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.